Created attachment 596552[details][diff][review]
Patch v1.
We're currently always passing the read-ahead flag (FILE_FLAG_SEQUENTIAL_SCAN) on Windows for every file operation.
This flag causes 1) old pages to be released faster and 2) extra data to be read before it is needed (if it is needed).
This is good in a lot of cases, but we should only use it when it is needed and when the flag is actually set.
I think it was unintentionally always turned on in October of 2011 in Bug 686691.